Conspiracy crossover
by NerdGurl89
Summary: Crossover with NCIS: Los Angeles. Castle gets a call from Alexis, who is visiting colleges in LA, and something is very, very wrong. He and Beckett get hurled into a world of espionage and conspiracies to get her back. Densi later if I feel like it.
1. Chapter 1

A/N: I know, I know. Why am I trying to write ANOTHER fic when I can't finish the ones I've already started? Answer: Because I know where this one is going...vaguely. More so than the other ones at least. Crossover with NCIS LA will come up in the next chapter, promise!

It's dark. Too dark. Dark like those school trips to caves on the outskirts of civilization, when they turn off all the lights and you can't see your hand in front of your face. It was scary then because you were young and the dark was full of the unknown, unnamed monsters and apparitions your friends told stories about to scare each other.

Except this girl is old enough that the monsters and apparitions are something she can name. Something experience and an unsheltered life have always warned her about. She feels that maybe, if she had listened closer, she wouldn't be in this all-consuming darkness, scared like a child in that cave again.

_Maybe the call went through_, she thinks. _This might be over soon._ She doubts it. The hours of isolation have worn her resolve.

"_Please Daddy..."_

* * *

><p>24 Hours Earlier...<p>

Castle groaned, eyes still closed, as he reached around for his vibrating phone. It was early, and when he finally opened his eyes a crack, he saw just how early. He groaned again.

3AM.

He was used to calls at all hours of the day and night; murder doesn't happen on a 9 to 5 schedule. But the night of drinking at the Old Haunt with Beckett, Lanie and the boys left him groggy and less inclined to move from his current position. Only his now almost constant need to see his partner dragged him upright.

"Hello."

He heard a chuckle over the phone at his raspy greeting.

"Got a body. Corner of 4th and Lex."

He cleared his throat and answered with a bit more clarity, "I'll bring the usual. Be there in 30."

They never had any need for more this early in the morning.

45 minutes later, Castle was hustling under the police tape outside a newsstand. It was still dark out, but he could see Kate roll her eyes as he jogged carefully forward, balancing her daily coffee and bearclaw.

"Fall asleep in the shower, Castle?"

He saw that playful grin play across her features, chasing away the annoyance at the hour.

"Ha ha, very funny. Mother caught me on my way out; wanted me to stop by the studio later and talk to her new play-write, you know, the one wrote her one-woman show."

"Gonna pass on some Castle pearls of wisdom?"

Castle squinted at her. "I sense sarcasm, Detective."

"Only sense? You're losing your touch."

She turned to the M.E., who Castle now saw was bending over a freshly murdered man in his late 40s. Stabbed, if he had to guess by the gashes in his chest and abdomen.

"We got a T.O.D., Lanie?"

"I'd estimate about 1 or 2 in the morning, this was very recent. And messy, guy was whaled upon."

"Overkill," provided Castle.

"Exactly. The killer blow was this one," she pointed with her pen at a gash near the center of his chest, "completely bisected the heart; he was dead within minutes. But nearly half of these," she pointed at a few more wounds on his chest, "were inflicted after death. No blood was lost. Your killer is going to be covered in blood, this stabbing was messy and it would've sprayed all over, as you can see by the spatters."

As Castle glanced at the spatters indicated by Lanie, he felt his phone vibrate in his back pocket. He stepped away towards the yellow tape so as to not interrupt Lanie and Beckett, and brought the phone to his ear.

He knew right away that something was very wrong.

On the other end, and he could see from glancing at the phone's screen that it was his daughter calling, he could hear ragged, uneven breathing.

"Alexis?"

"_Da-Dad_." The service was cutting in and out. "_Dad...Don't...where...aken...dark..."_

Static.

"Alexis!"

Beckett had taken notice of his absence and wondered over. At the sight of his alarmed face, she mimed asking what was wrong.

He shook his head, focusing on the sound in his right ear.

"Alexis!" he called again.

"_...rine...LA...ble's Bar...something ba...I'm so sorr..._

_Please Daddy_."

And then the line went dead.


	2. Chapter 2

A/N: Here's Chapter 2! Chapter 3 will come pretty quickly, I've got most of it planned out in my head. The balls starting to get rolling here, and NCIS LA finally joins in! Chapters should start to get longer as I go along. Enjoy! And REVIEW!

* * *

><p>"Castle, breathe and tell me what happened."<p>

Rick Castle's mind was in overdrive. All he knew was that his daughter was in trouble, and on the other side of the country. The only things keeping him from speeding to the airport that second were his partner's hands on his shoulders, firm and commanding.

Glaring at her for keeping him stationary, he followed her instructions and took several calming breaths.

"It was Alexis. I couldn't hear everything she was saying, it kept cutting out, but I know she's in trouble. I need to get on a plane..." He tried to free himself from her grip, and once again found her grip firm.

"Hold on Castle, first, where is she exactly?"

Castle was almost incandescent with rage. A small part of his brain told him that it wasn't her fault, that maybe she could help. This small sane thought gave him the calm to answer.

"Alexis went to stay with Meredith over spring break to visit colleges there. I knew is should've gone with her! Meredith can't-"

"Castle!"

He stopped mid-sentence, glowering again.

"Call Meredith. Make sure you didn't hear wrong and that Alexis isn't sitting safe and sound at her mom's. She won't thank you for barging in, guns blazing."

He knew she was right, and it pissed him off. Still holding her gaze, he dialed Meredith's cell.

"Rick?"

"Meredith, where's Alexis?"

Silence. Then,

"I guess she's in her room. She went out with some friends she made at one of the college visits, said she'd be back late."

"And you _didn't_ wait up for her."

"I have a screen test today, I needed my beauty sleep! Why?"

"Get up and check that she is in her room."

"Ricky-"

"Do it, Meredith."

Kate's P.O.V.

His voice was hard. Kate only ever saw her partner like this when it came to his daughter. He was soft and gooey until Alexis was hurting; then he became dangerous to any who stood in his way. Except for herself, apparently. She knew this was because Castle valued her opinion enough to listen before jumping blindly into action.

She saw his face get even paler, if that were possible. He hung up the phone and closed his eyes, breathing through his nose like a bull.

"She wasn't there." She said. It wasn't a question. She could see the truth all over his face.

"I have to go to LA."

"I know." And she did. She also knew what she had to do.

"I'm coming with you."

"The case..."

"It's open and shut Castle. Ryan and Esposito are canvasing with unis, the murderer won't be hard to miss covered in all that blood. They can handle it. And I want to be there to help if you need it." She watched his face relax somewhat at her statement. Not completely, but his jaw loosened slightly. It wasn't entirely true, she had no idea if the case was going to be easy or not, but her boys were capable, and Castle needed her.

An hour and a half later, she and Castle were seated in First Class on the way to LA. He hadn't relaxed any more than that little bit when she told him she was coming with him, and she knew he wouldn't completely until he saw his little girl in front of him, safe and sound. He was gripping the armrests impatiently, watching the clouds go by out of the tiny window.

It was this side to him that made Kate weak in the knees when she least expected it. It wasn't the only thing about him that attracted her, but his bouts of fatherly affection and adoration always caught her off guard. He was fierce father, and she loved that about him.

Kate put her hand over her partner's; his grip loosened on the armrest. He turned his hand over, lacing their fingers. It was becoming somewhat of a habit for them, holding hands. Not something they talked about necessarily, but an unspoken form of comfort and solidarity. And she could handle that for now, while her secret remained hidden. So she held on, wishing she could send strength to Castle through their clasped hands.

* * *

><p>Los Angeles, California; NCIS: OSP Headquarters<p>

Marty Deeks checked to make sure his companion was still following at his heels as he entered the office. Sure enough, Monty was sticking close, tongue hanging out in his goofy grin. He seemed to enjoy coming to work with him at NCIS, more so now that Sam had a soft spot for him.

"Monty!"

The shaggy dog's ears perked up as Kensi called to him from her desk. He bolted without a second look at his master. Deeks puffed a laugh, shaking his head. He was cup in the chair with her, licking her face.

"That dog just uses you to get to her," Callen said, taking his seat with a full cup of coffee. "We all know where his real loyalties lie."

"Ha, yeah. Speaking of which, Kens, can Monty stay at your place for a couple of days? They're spraying for bugs and I don't want him getting sick.."

Monty stopped licking and looked at Kensi, almost as if he were waiting for an answer too.

"Sure, only because I can't say no to that face..."

Deeks grinned, feeling pleased.

"Isn't that right Monty?"

Callen and Sam laughed at the look on Deeks' face.

A whistle sounded from above, causing Monty to start barking.

"Ladies, Gentlemen, and...Monty. We've got a case!"

When they had all piled into Ops, Nell began.

"Corporal Derek Mills, 34, was recruited to a Military think-tank in LA when he was only 20 years old. Genius IQ, and put in charge of finding solutions to government problems, from the economy to terrorism to monitoring which party will win the next election. He has his fingers in _every _pie."

"Why are you telling us this?" Sam asked, curious.

"Because as of 3 days ago, Corporal Mills has gone AWOL," answered Eric. He brought up a copy of the Coporal's file. "Apparently this isn't the first time, according to his yearly psych eval he wasn't feeling appreciated, and he would frequently leave for up to 24 hours. This is the longest he's been gone, and with the information in his head..."

"Whoever has him could bring down our entire government," finished Callen. "What about his cell?"

A few clicks, more information was brought up onscreen, along with a map. "His phone is off, but last night he made a call to his voicemail. Traced it to this," a dot appeared with an address, "Gable's bar and grill on Sunset. Address on your phones."

Callen turned to his team. "Sam and I will check out the bar, Kensi, you and Deeks go search his apartment."

Hetty stopped them at the door. "I don't think I need to impress the need for a swift and clean resolution to this case, but I will; do it right, and do it quickly." She looked at each of them in turn. "What this man knows could destabilize more than just this country. Keep me apprised." She moved to let them pass.

* * *

><p>Kate's POV<p>

The flight had passed in silence. Castle seemed to snap out of his panicked stupor in the terminal, and seemed to pull himself together a bit.

"Do you think we could get a hold of that LAPD detective we worked with on Royce's case?"

Kate nodded; she had been thinking the same thing. "Yeah, Detective Seeger. I'll call LAPD and see if they can reach him."

Luckily for them, Seeger was stuck inside doing paperwork. "Why, Detective Beckett. Not going rogue again I hope."

"Not exactly. Castle's daughter's gone missing." She glanced up at him; he was watching her with an unreadable expression.

"I'm sorry to hear that, but I don't know what I can do to help from the other side of the country."

"She was visiting colleges in LA. Castle got a call from her around 4 this morning. It was broken up, but it sounded like something was wrong."

"Where was she staying?"

"With her mom, who hasn't seen her since last night."

Silence. Then,

"Ok, how can I help?"

Kate held Castle's gaze when she answered. "I know we don't have jurisdiction or even an actual case, but...this is his _daughter._ If you could just run her phone and credit records, maybe see where she went last night...Castle can give you her details, and I would owe you big time."

"Pass him over."

Kate handed the phone to Castle, registering in the back of her mind that they were still clasping hands. Any other day this would either thrill her or cause her to run for the hills, but today she was just worried.

After giving the LAPD detective his daughter's information, he handed the phone back without a word. She thanked Seeger once again and hung up. Then turned to her partner, clasping his forearms, but gently this time.

"We _will_ find her, Castle."

He almost smiled. Almost.

"Thank you, Kate. For coming with me."

"Always." She smiled tightly.

* * *

><p>AN: Now, PLEASE REVIEW! Let me know if I'm getting the voices and tone right.


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